clarify artifice postprocessor wording to make it clear that it will not clean up old artifacts (#8676)

fix #5451

post-processor/artifice/post-processor.go

@@ -56,7 +56,7 @@ func (p *PostProcessor) Configure(raws ...interface{}) error {
 
 func (p *PostProcessor) PostProcess(ctx context.Context, ui packer.Ui, artifact packer.Artifact) (packer.Artifact, bool, bool, error) {
 	if len(artifact.Files()) > 0 {
-		ui.Say(fmt.Sprintf("Discarding artifact files: %s", strings.Join(artifact.Files(), ", ")))
+		ui.Say(fmt.Sprintf("Discarding files from artifact: %s", strings.Join(artifact.Files(), ", ")))
 	}
 
 	artifact, err := NewArtifact(p.config.Files)

website/source/docs/post-processors/artifice.html.md

@@ -33,6 +33,10 @@ stateless build environment for each build on the infrastructure of your
 choosing. You can use this to build just about anything: buildpacks,
 containers, jars, binaries, tarballs, msi installers, and more.
 
+Please note that the artifice post-processor will _not_ delete your old artifact
+files, even if it removes them from the artifact. If you want to delete the
+old artifact files, you can use the shell-local post-processor to do so.
+
 ## Workflow
 
 Artifice helps you tie together a few other packer features: